MIH prevalence varies between 2.9% and 44% in different countries4. In Spain it ranges between 12.4% and 21.8%8,32,33, with 24.2% observed in the present study. MIH is most often encountered in a mild form8,10,12,15,24,33,34,35,36,37, which agrees with the results of the present study, where 72% of the MIH cases were mild and 28% severe.
Most authors have concluded that there is a relationship between hypomineralized teeth and dental caries8,10,11,15,16,17,18,19,20,21,22. However, others have stated that hypomineralization does not predispose towards caries in hypomineralized teeth23,24,25. In the present study, no statistically significant differences in caries prevalence were found between children with MIH (irrespective of level) and without MIH (48% and 45.5% respectively). However, on distinguishing between different levels of MIH, the severe MIH cases had significantly higher caries prevalence than those with mild MIH (60.7% and 43.1% respectively, p = 0.0251), which would indicate that more severe MIH entails a higher susceptibility to caries.
In the present study, as in Heitmuller et al.25, no statistically significant differences in DMFS between children with no MIH and those with mild MIH were observed. Few previous studies have distinguished between different levels of MIH when assessing differences in caries scores. In the present case, the caries scores were significantly higher in children with severe MIH compared to those with mild MIH or no MIH. Also, a linear tendency was found in mean DMFS scores, which rose as the severity of the hypomineralization increased.
It has been said that one of the main risks of observational bias when studying the relationship between MIH and caries is that the examiner who records the presence or absence of caries is necessarily also seeing the presence or absence of MIH, and vice versa, hence the recommendation that MIH and caries be assessed by two different examiners38. In this study, the MIH and caries evaluations, the latter using the ICDAS criteria, were conducted independently by two separate observers after calibration in the respective methods.
Several studies have shown that children with MIH need more dental treatment (whether urgent, non-urgent or preventive) than those without MIH8,11,15,16,18,39. MIH has an impact on increased caries prevalence and on restoration work in permanent first molars16,18. The higher scores for DMFS and its F component obtained in the present study confirm that children with severe MIH need more fillings.
The tooth-surface caries ratio rises as the severity of hypomineralization increases5. This could be because opacities in the cream to brown color range are more porous5 and more susceptible to PEB, and PEB, in turn, exacerbates the caries and increases its severity. Kosma et al.22 observed that the more severe the MIH the greater the caries, which agrees with Pitiphat et al.20, who found that caries lesions are 10 times more frequent in teeth with PEB (severe MIH) than in teeth that only have opacities (mild MIH). Elfrink et al.40 observed that the mean density of the hydroxyapatite in opacities in the yellow to brown color range is 20% to 22% lower than in sound enamel, while the difference is almost nonexistent in white opacities. The results of the present study have also shown that the caries is far greater in surfaces with severe MIH than in surfaces with mild MIH or no MIH.
The variability in the results of studies that have investigated the relationship between MIH and dental caries suggests the need for a standard protocol that would allow comparative analysis and strengthen the evidence for the conclusions. The present study followed the MIH diagnostic criteria established by EAPD3, which agree with the current guidelines proposed at the 12th EAPD Congress held in Sopot (Poland) in 2014 and published by Elfrink et al.4 and Ghanim et al.28.
This study provides detailed information on the caries status of teeth with MIH, distinguishing between caries in surfaces with mild hypomineralization or with severe hypomineralization in order to measure which level of the disease has a greater association with MIH. Caries was measured in the occlusal, labial and palatal/lingual surfaces of molars and incisors, the teeth that are liable to MIH. Other authors have also examined for caries in interproximal surfaces8,10,35,41 but these cannot be examined for MIH, which could lead to underestimating the relationship between MIH and caries. Also, in the present authors’ opinion, studies that include all the teeth8,17,19,20,21,25,42,43,44,45,46 can skew the results because of the greater number of teeth and because they cannot be compared with the index teeth for MIH.
As regards caries diagnosis, the criteria used in the different studies have also differed: most have followed the WHO criteria8,15,16,17,19,20,21,22,24,39,42 and very few have used ICDAS18 or the Universal Visual Scoring System25. The lack of agreement between the ICDAS29,30 and WHO47 diagnostic criteria could make it difficult to achieve an adequate assessment of the epidemiological trend in dental caries, which is why the EAPD prescribed the use of ICDAS II for caries prevalence studies48. The ICDAS II system enables initial stages of caries to be coded, unlike the WHO system, which only scores active caries lesions (ICDAS II codes 4, 5 and 6) and therefore underestimates the level of caries.
Some authors do not include filled teeth in their DMF scores if they believe them to be associated with atypical caries due to MIH25, and therefore obtain lower DMF values, but most atypical restorations in teeth affected by MIH have involved a history of caries even if it cannot be established with certainty at the time of examination. Consequently these authors could be underestimating the DMF, while those who include all fillings in the DMF could be overestimating it. In the present study, following the EAPD criteria3, extensive or atypical restorations were included in the MIH diagnosis if they had opacities around the edges or on another surface of the tooth or if MIH criteria applied to another molar.
Diet and oral hygiene play an important role in the etiological factors of caries and the present study observed a rise in mean DMFS as the intake of cariogenic foods increased. The multifactorial analysis found that cariogenic food intake and the presence of severe MIH were significantly related to higher DMFS scores, but that mild MIH showed no association with dental caries.
Preventive measures against dental caries involve improving oral hygiene and changing the child’s dietary habits. Applying fluoride as a varnish or in trays, and in toothpaste or rinses, is also effective. Nevertheless, it is also important to treat active lesions, whether by remineralizing an incipient or chronic lesion or by filling a cavitated lesion. It is very important to monitor teeth with signs of MIH to avoid their premature loss from dental caries, examining primary molars for hypomineralization and, if they are affected, monitoring the development of the permanent first molars49. These children should also be included in a high caries risk follow-up protocol.
The present study examined the association between MIH and dental caries and found an association between dental caries and the presence of surfaces affected by severe MIH, which should be considered a risk factor within the multifactorial etiology of caries.